Tutorial 2 - The Queries

Edit 0 11 …

Queries

In these example, the variable "em" is an entity manger initialized just like it was in the first tutorial.

Empty String
Setup: None required
  • em.createQuery("");

Unknown Class
Setup: None required
  • em.createQuery("from IncorrectClassName");

Minimal "Get All"
Setup: None required
  • em.createQuery("from Person").getResultList();

Successfully Get a Single Object
Setup: Insert exactly 1 Person entity in the database
  • final Person p = (Person) em.createQuery("from Person").getSingleResult();

Unsuccessfully Try to get a Single Object When There Are None
Setup: Make sure there are no Person entities in the database
  • em.createQuery("from Person").getSingleResult();

Unsuccessfully Try to get a Single Object With Too Many
Setup: Insert two or more Person entities in the database
  • em.createQuery("from Person").getSingleResult();

Find By Primary Key
Setup: Insert a Person in the database, make sure to get the key of the object inserted
  • final Person p = em.find(Person.class, personKey);

Unsuccessfully Find by Primary Key
Setup: None required
  • final Person p = em.find(Person.class, -42);

Search Using Query Parameter and Storing Result as List<?>
Setup: Insert one person record where the Person's first name = "Brett".
    final List<?> list = em.createQuery("from Person where p.firstName = ?1")
        .setParameter(1, "Brett").getResultList();

Search Using Query Parameter and Storing Result as List<Person>
Setup: Insert one person record where the Person's first name = "Brett".
    final List<Person> list = em.createQuery(
        "from Person where firstName = ?1").setParameter(1, "Brett")
        .getResultList();

Do Find by Primary Key and Queries Return == Objects
Setup: Insert one person record and store the primary key. Also make sure the first name of the person equals "Brett".
    final Person pByKey = em.find(Person.class, personKey);
 
    final Person pByWhere = (Person) em.createQuery(
        "SELECT p from Person p where firstName='Brett'")
        .getSingleResult();

Use Wrong Class Name
Setup: None required
  • em.createQuery("from PERSON").getSingleResult();

Use Wrong Field Name
Setup: None required
  • em.createQuery("from Person p where p.FirstName='Brett'");

Use Column Name Instead of Field Name
Setup: None required, but maybe insert a single person whose first name = "Brett".
  • em.createQuery("from Person p where p.firstName='Brett'").getResultList();

Use a Parameter but Provide Wrong Index
Setup: None required
  • em.createQuery("from Person p where p.firstName=?1").setParameter(0, "Brett");

Set Parameter Where There are None: Version 1
Setup: None required
  • em.createQuery("from Person p where p.firstName='Brett'").setParameter(1, "Brett");

Set Parameter When There Are None: Version 2
Setup: None required
  • em.createQuery("from Person p where p.firstName='?1'").setParameter(1, "Brett");